Question

The compound(s) showing optical activity is/are

• A.
• B.
• C.
• D.

Hint:

Using a simple frame or just bolding for the box
Key Points:
Optical activity requires chirality (non-superimposable mirror image).
Presence of a chiral center (carbon with 4 different groups) usually leads to chirality.
Exception: Meso compounds have chiral centers but are achiral due to internal symmetry (e.g., a plane of symmetry).
Glycine (A) is achiral. Lactic acid (B) and Glyceraldehyde (C) are chiral.
Tartaric acid (D) exists as chiral enantiomers and an achiral meso form. The diagram shows the meso form, but the compound name itself includes optically active forms.

Answer 1

The Correct Option is B

Chiral molecules, which are non-superimposable on their mirror images, exhibit optical activity. A chiral center (a carbon atom bonded to four different groups) commonly causes chirality.\n\n

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• (A) Glycine: The central carbon atom bonds to two hydrogen atoms, a carboxyl group (-COOH), and an amino group (-NH₂). Having two identical groups (H) makes it achiral and optically inactive.
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• (B) Lactic Acid: The central carbon atom (C2) is bonded to four distinct groups: hydrogen (-H), hydroxyl (-OH), methyl (-CH₃), and carboxyl (-COOH). Thus, C2 is a chiral center, rendering lactic acid chiral and optically active.
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• (C) Glyceraldehyde: The central carbon atom (C2) is bonded to four different groups: hydrogen (-H), hydroxyl (-OH), aldehyde (-CHO), and hydroxymethyl (-CH₂OH). Therefore, C2 is a chiral center, and glyceraldehyde is chiral and optically active.
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• (D) Tartaric Acid: This molecule has two potential chiral centers (C2 and C3), each bonded to H, OH, COOH, and the other C(H)(OH)COOH group.\n
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  • The depicted Fischer projection shows a plane of symmetry between C2 and C3 (the top half is the mirror image of the bottom half), representing meso-tartaric acid. This form is achiral due to internal compensation and is thus optically inactive.
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  • Tartaric acid also exists as two chiral enantiomers ((+)-tartaric acid and (-)-tartaric acid), which lack this symmetry and are optically active.
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  • Since the question asks about optical activity, and tartaric acid can exist in optically active forms, this option is likely correct considering its potential isomers, despite the specific meso structure.
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